An ’80 4-door F body and ’80 4-door M-body are very similar – with a few differences (like header panel, dash design, taillights, etc.).
The ’80 police version of F and M-body suspensions are exactly the same.
It was mentioned earlier but the differences between (all) police and non-police FMJ-body suspensions are:
- Front sway bar is larger.
- Front sway bar to K-frame brackets are different (different size sway bar inner and outer bushing diameters).
- Torsion bars are exactly the same – but the rubber bushings (K-frame mount and control arm mount) are firmer. The police bushings have been out of production sense the early ‘90’s. The normal/regular bushings are getting few and far between, now days.
- There is a rumor the police K-frames are stronger. I have had police and non-police K-frames side by side and can’t see any differences between then (so maybe different, but I doubt it). If you have a K-frame out of car and considering driving hard with it, I do highly recommend making sure everything is welded up on K-frame with extra gussets, etc. to beef it up.
- Rear leaf springs are 5-leaf. Most (not all) Wagons, police and some towing package cars use 5-leaf springs. All others use 4-leaf springs.
Note: 4-leaf and 5-leaf ISO-clamp lower brackets are different (to allow the thickness of the additional spring).
- Rear sway bar (a police car only (or aftermarket), item).
- Rear leaf spring shackle are trapezoid shaped instead of rectangular shaped. Note: the frame bracket for rear leaf spring is also different because of the wider (at frame side) trapezoid shaped shackles.
Police shackle (looking from front of car rearwards).
Non-police shackle
Note: you can see the police frame bracket "tube" is wider, than the lower version is.
If you have access to F or M-body police suspension parts – then great. If not, then aftermarket parts might be better. The parts from FFI (Firm Feel)
http://www.firmfeel.com/fmj_body_mopar_parts.html are great - but pricey.
I have an ’77 F-body and a ’86 M-body and still gathering parts for both. I also have the complete front and rear suspension systems from a rusted out ’84 Gran Fury police car.
My plans (for both vehicles), is to use torsion bars (which are thicker/stronger), front and rear sway bars from FFI. Use either aluminum (or iron or urethane) K-frame mounts (FFI or other). 5-leaf rear springs (my wagon already has 5-leaf). Get rid of the rear suspension ISO-Clamp and replace with older style shock brackets (note: others have had good luck by replacing the ISO-Clamp rubber with urethane biscuits – but the lower ISO metal bracket is prong to failure - see picture, below).
Lastly, use either a FFI or Borgeson steering gear.
For brakes, there is an upgrade to using Jeep rear disk brakes, and upgrade to using ’75-81 B and R-body 11¾” front brake rotors (FMJ’s use 11” diameter front rotors). The additional ¾” doesn’t sound like much – but they work better. The 11¾” brake rotors as well as the Jeep rear disks do require 15” wheels (or larger).
The same if you were to use 11” rear drum brakes (which is also comes with police or towing package cars) – for they also require 15” (or larger) wheels.
You DO NOT want your rear brakes to over- power the front brakes – or bad things
will happen.
To be honest – I love the idea of the Jeep rear disk brake setup, as well as 11” drum brakes,
BUT not until you upgrade your front brakes, first!
FFI aluminum K-frame mounts
Rear shock plates. These are aftermarket - but older factory parts look close. These replace the rear ISO-Clamps and do require a different rear shock ('66-72 B-body) and longer U-bolts.
The blue circle is where the lower ISO-clamp fails at (note to self: get a better picture than this).
I hope this helps.
BudW
